Method of making a thermocolor ribbon for a thermal printing process

Abstract

A thermal transfer meltable color layer receives a protective polymer coating on the side thereof, to be contacted with the thermal printing head to hold the meltable color material away from the printing head, thereby forming a thermal printing ribbon without the need for a support foil.

We claim: 
     
       1. A method of making a thermal-transfer ribbon having no support foil, which comprises the steps of: (a) forming a transfer layer composed of at least one binder selected from the group which consists of waxes and plastic materials and at least one coloring agent incorporated in said binder, said transfer layer melting upon heating to a melting temperature to transfer a portion of said layer in a symbol pattern;   (b) depositing said transfer layer onto a temporary support;   (c) applying to one side of said transfer layer, a protective polymer layer by coating said side of said transfer layer with a solution or dispersion of a film-forming polymer nonmeltable at said melting temperature in a solvent or dispersing medium, and evaporating said medium from said solution or dispersion; and   (d) removing from said temporary support said thermal-transfer ribbon consisting of said transfer layer and said protective polymer layer.   
     
     
       2. The method defined in claim 1 wherein, in step (c), a solution of a nonmeltable film-forming polymer is coated onto said side of said transfer layer. 
     
     
       3. The method defined in claim 2 wherein said solution of a nonmeltable film-forming polymer is an aqueous solution of a polymer. 
     
     
       4. The method defined in claim 3 wherein said aqueous solution of a polymer is formed from at least one polymer selected from the group which consists of polyvinylpyrrolidone and polyvinylalcohol. 
     
     
       5. The method defined in claim 1 wherein, in step (c), an aqueous dispersion of a polymer is coated onto said side of said transfer layer. 
     
     
       6. The method defined in claim 1 wherein said protective polymer layer is formed in step (c) on said transfer layer with a thickness of substantially 0.5 to 12 micrometers. 
     
     
       7. The method defined in claim 11 wherein said protective polymer layer is formed in step (c) on said transfer layer with a thickness of substantially 0.5 to 6 micrometers. 
     
     
       8. The method defined in claim 1 wherein said protective polymer layer is formed in step (c) on said transfer layer as an electrically conductive layer. 
     
     
       9. A thermal-transfer ribbon made by the method of claim 1. 
     
     
       10. The method defined in claim 1 wherein, after step (d) said thermal-transfer ribbon is wound in a roll so that said roll can be used directly in a thermal printing system.